We present GHRS/HST observations of the RS CVn binary system HD 155555. Several key UV emission lines (Fe XXI, Si IV, O V, C IV) have been analyzed to provide information about the heating rate throughout the atmosphere from the chromosphere to the corona. We show that both the G and K components reveal features of a chromosphere, transition region and corona. The emission measure distribution as a function of temperature for both components is derived and compared with the RS Cvn system, HR 1099, and the Sun. The transition region and coronal lines of both stars show nonthermal broadenings of approx. 20-30 km/s. Possible physical implications for coronal heating mechanisms are discussed.